fix(combobox-web): fix inverted editability logic in getReadonly

The `conditionally` branch returned `expression.value` directly, so a
truthy value (meaning "editable") made the widget read-only, and vice
versa.  Fixed by returning `true` only when the expression is not `true`,
and added unit tests for all `getReadonly` branches.

Author: r0b1n

packages/pluggableWidgets/combobox-web/CHANGELOG.md

@@ -12,6 +12,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 - We fixed an issue where the widget crashed when using the "On filter input change" action with the new string behavior enabled.
 
+- We fixed an issue where the custom editability condition (`never` or `conditionally`) was ignored when the combobox attribute was present and editable.
+
+- We fixed an issue where the editability setting was inverted: setting editability to `false` allowed editing, and setting it to `true` prevented editing. The editability condition expression now behaves correctly: `true` means editable, `false` means read-only.
+
+### Breaking changes
+
+- The editability fix above is a potential breaking change. Apps that worked around the bug by inverting their editability expression will now have the opposite (incorrect) behavior after upgrading. Review any combobox widgets using a custom editability expression and remove the inversion workaround, otherwise fields may unexpectedly become editable or read-only.
+
 ## [2.8.1] - 2026-04-30
 
 ### Fixed

packages/pluggableWidgets/combobox-web/src/helpers/Database/__tests__/utils.spec.ts

@@ -0,0 +1,156 @@
+import Big from "big.js";
+import { EditableValue } from "mendix";
+import { dynamic, EditableValueBuilder } from "@mendix/widget-plugin-test-utils";
+import { getReadonly } from "../utils";
+
+describe("getReadonly", () => {
+    describe("when targetAttribute is readOnly", () => {
+        it("is read-only regardless of customEditability 'default'", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").isReadOnly().build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "default",
+                dynamic.available(true)
+            );
+
+            expect(result).toBe(true);
+        });
+
+        it("is read-only regardless of customEditability 'never'", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").isReadOnly().build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "never",
+                dynamic.available(true)
+            );
+
+            expect(result).toBe(true);
+        });
+
+        it("is read-only regardless of customEditability 'conditionally' with expression true", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").isReadOnly().build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "conditionally",
+                dynamic.available(true)
+            );
+
+            expect(result).toBe(true);
+        });
+    });
+
+    describe("when targetAttribute is editable", () => {
+        it("is editable when customEditability is 'default'", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "default",
+                dynamic.available(true)
+            );
+
+            expect(result).toBe(false);
+        });
+
+        it("is read-only when customEditability is 'never'", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "never",
+                dynamic.available(true)
+            );
+
+            expect(result).toBe(true);
+        });
+
+        it("is read-only when customEditability is 'conditionally' and expression value is false", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "conditionally",
+                dynamic.available(false)
+            );
+
+            expect(result).toBe(true);
+        });
+
+        it("is editable when customEditability is 'conditionally' and expression value is true", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "conditionally",
+                dynamic.available(true)
+            );
+
+            expect(result).toBe(false);
+        });
+
+        it("is read-only when customEditability is 'conditionally' and expression is loading", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "conditionally",
+                dynamic.loading()
+            );
+
+            expect(result).toBe(true);
+        });
+
+        it("is read-only when customEditability is 'conditionally' and expression is unavailable", () => {
+            const targetAttribute = new EditableValueBuilder<string>().withValue("value").build();
+
+            const result = getReadonly(
+                targetAttribute as unknown as EditableValue<string | Big>,
+                "conditionally",
+                dynamic.unavailable()
+            );
+
+            expect(result).toBe(true);
+        });
+    });
+
+    describe("when targetAttribute is undefined", () => {
+        it("is read-only when customEditability is 'never'", () => {
+            const result = getReadonly(undefined, "never", dynamic.available(true));
+
+            expect(result).toBe(true);
+        });
+
+        it("is editable when customEditability is 'default'", () => {
+            const result = getReadonly(undefined, "default", dynamic.available(false));
+
+            expect(result).toBe(false);
+        });
+
+        it("is read-only when customEditability is 'conditionally' and expression value is false", () => {
+            const result = getReadonly(undefined, "conditionally", dynamic.available(false));
+
+            expect(result).toBe(true);
+        });
+
+        it("is editable when customEditability is 'conditionally' and expression value is true", () => {
+            const result = getReadonly(undefined, "conditionally", dynamic.available(true));
+
+            expect(result).toBe(false);
+        });
+
+        it("is read-only when customEditability is 'conditionally' and expression is loading", () => {
+            const result = getReadonly(undefined, "conditionally", dynamic.loading());
+
+            expect(result).toBe(true);
+        });
+
+        it("is read-only when customEditability is 'conditionally' and expression is unavailable", () => {
+            const result = getReadonly(undefined, "conditionally", dynamic.unavailable());
+
+            expect(result).toBe(true);
+        });
+    });
+});

packages/pluggableWidgets/combobox-web/src/helpers/Database/utils.ts

@@ -99,14 +99,14 @@ export function getReadonly(
     customEditability: ComboboxContainerProps["customEditability"],
     customEditabilityExpression: ComboboxContainerProps["customEditabilityExpression"]
 ): boolean {
-    if (targetAttribute) {
-        return targetAttribute.readOnly;
+    if (targetAttribute?.readOnly) {
+        return true;
     }
     if (customEditability === "never") {
         return true;
     }
-    if (customEditability === "conditionally") {
-        return customEditabilityExpression.value ?? true;
+    if (customEditability === "conditionally" && customEditabilityExpression.value !== true) {
+        return true;
     }
     return false;
 }